Pereboev D.D.*, Kotov A.A. 2026. Evolutionary history of the subgenus Daphnia (Ctenodaphnia) Dybowski et Grochowski, 1895 (Crustacea: Cladocera), inferred from a phylogenomic study of D. (C.) studeri (Rühe, 1914) // Arthropoda Selecta. Vol.35. No.3: 293–302 [in English].
A.N. Severtsov Institute of Ecology and Evolution, Leninsky Prospect 33, Moscow 119071 Russia.
*Corresponding author
Dmitry Pereboev: dm.pereboev@gmail.com; https://orcid.org/0009-0004-8194-7585
Alexey Kotov: alexey-a-kotov@yandex.ru; https://orcid.org/0000-0002-8863-6438
doi: 10.15298/arthsel.35.3.03
ABSTRACT. Subgenus Daphnia (Ctenodaphnia) Dybowski et Grochowski, 1895 (Crustacea: Cladocera) is a diverse group inhabiting a wide range of biotopes spreading from the Arctic to the Antarctic. D. (C.) studeri (Rühe, 1914) is one of only two species of Cladocera present in continental Antarctica, it is also distributed in Subantarctic islands. Earlier research showed that this species is closely related to D. atkinsoni s.l., an example of the so-called “crowned” D. (Ctenodaphnia) having a “crown of thorns”, a protective structure induced by the presence of predators. Moreover, D. (C.) studeri was earlier placed in “Daphniopsis Sars, 1903” genus with another protective structure, the caudal needle, being highly reduced or absent. We performed phylogenomics and mitogenomic analyses to explore evolutionary history of D. (C.) studeri. In the mitogenomic analyses, the D. (C.) atkinsoni species group (D. atkinsoni s.l. and D. studeri) is monophyletic and D. studeri appears in the sister position to D. atkinsoni s.l. On the other hand, in the nuclear phylogeny D. atkinsoni s.l. is paraphyletic with respect to D. studeri. However, based on the morphological and mitogenomic evidence, and the results of the concordance factor analysis, we believe that the latter result is possibly an artefact.
According to fossil-calibrated dating based on mitogenomes, divergence of the D. (C.) atkinsoni species group and the closest outgroup, D. (C.) tibetana, happened ca. 80 MYA, and divergence of D. (C.) studeri and D. (C.) atkinsoni s.l. happened ca. 60 MYA. Such dates correspond well to the time of existence of the Oman–Kohistan–Ladakh Arc (~80–55 MYA), a hypothetical route between India and North Africa, possibly used by the earlier lineages for their dispersal. Moreover, an ancestor of D. (C.) studeri could have passed south via Kerguelen and Ninetyeast Ridge route, which had been open since the Late Cretaceous. Tracing the evolution of protective structures, we can hypothesize that their loss was associated with colonisation of refugial habitats (extreme arid regions with saline waters, high mountains of Tibet and Antarctic-sub-Antarctic regions). Such habitats lack most predators, including small-sized invertebrates, against which protection is provided by the caudal needle and the “crown of thorns”.
KEY WORDS: Branchiopoda, protective structures, phylogeography, phylogeny, Antarctic.
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